Synchronized delivery of Er:YAG-laser-pulse energy during oscillations of vapor bubbles

A laser system and a measuring method for the synchronized delivery of multiple Er:YAG-laser pulses during vapor-bubble oscillations are presented. We use a free-running Er:YAG laser, designed for laser dentistry. Our results reveal that for short Er:YAG laser pulses, spherical bubbles develop even if a flatend fiber tip is used for delivery of the Er:YAG-laser pulses into water. We developed a method called a laser-beamtransmission probe for on-line monitoring of the bubbles’ oscillations. By using this method combined with shadowgraphy, we show that the dissipation of the bubbles’ energy during bubble oscillations can be efficiently balanced by the synchronized delivery of multiple Er:YAG-laser pulses. Our results show that the resonance effect is obtained when the second laser pulse is delivered at the end or slightly after the bubble’s collapse. In this case the resonance effect increases the mechanical energy of the secondary oscillations. The presented PHAST (Photo Acoustic Synchronized Transients) method has great potential to open new opportunities for further development of modern laser-based dental treatments.